Many solid catalyst components have heretofore been proposed, which comprise, as the essential catalyst ingredients, magnesium, titanium, halogens and electron donors. It is well known that these catalysts display high activity in olefin polymerization, and exhibit high stereospecificity in polymerization of .alpha.-olefins. In particular, it is known that solid catalyst components comprising, as electron donors, aromatic esters such as typically phthalates have excellent catalytic capabilities. However, using aromatic compounds is often disliked because of their problems of safety and hygiene.
Using malonate derivatives as non-aromatic electron donors has been proposed. For example, in Japanese Patent Publication No. 80044/1992, proposed are compounds of a general formula (II): ##STR2##
wherein either one or both of R.sup.3 and R.sup.4 are linear or branched hydrocarbon groups each having 4 carbon atoms, or aromatic hydrocarbon groups. However, using the compounds does not provide satisfactory stereospecificity in polymer production. In Japanese Patent Laid-Open No. 122716/1994, proposed are compounds of formula (II) where R.sup.3 and R.sup.4 are bonded to each other to form a cyclic structure. In Japanese Patent Laid-Open No. 279517/1994, proposed are compounds of formula (II) where R.sup.3 and R.sup.4 are both hydrogen atoms; those where either one of R.sup.3 and R.sup.4 is a linear or branched hydrocarbon group having at least one carbon atom, or an aromatic hydrocarbon group, and where the other is a hydrogen atom; and those where both R.sup.3 and R.sup.4 are linear hydrocarbon groups each having at least 2 carbon atoms. However, using the compounds provides extremely poor yields of polymers. In Japanese Patent Laid-Open No. 157521/1996, proposed are compounds of formula (II) where both R.sup.3 and R.sup.4 are branched or cyclic hydrocarbon groups each having at least 3 carbon atoms. However, the malonates having such branched or cyclic hydrocarbon groups are difficult to produce, and, in addition, using them provides poor yields of polymers and is therefore impracticable. In Japanese Patent Laid-Open Nos. 124705/1991 and 168207/1991, using other non-aromatic diesters as electron donors is proposed. However, the non-aromatic diesters proposed are not always satisfactory for providing a high yields of stereospecific polymers.
The object of the present invention is to provide solid catalyst components for olefin polymerization, catalysts for olefin polymerization and processes for producing olefin polymers, for which are used, as electron donors, compounds having no problems of safety and hygiene. The compounds for electron donors are inexpensive and are easy to produce, and display high activity and high stereospecificity in olefin polymerization.